Process for the preparation of a dop-containing mixture

ABSTRACT

The invention relates to a process for the preparation of 2&#39;-hydroxydiphenyl-2-phosphinic acid in the form of a commercial mixture with 6-hydroxy-(6H)-dibenzo-(c,e)(1,2)-oxaphosphorine, the process being carried out on a commercial scale, more simply and more cheaply than previously, as a one-pot reaction without isolating intermediate products and avoiding a distillation step, with said process comprising the steps: 
     (a) o-phenylphenol is added to a mixture of PCl 3  and a Lewis acid as a catalyst while simultaneously heating the reaction mixture, and the reaction mixture is then fluxed; 
     (b) the resulting reaction mixture is allowed to cool and, stirring continuously, is hydrolysed, being mixed first with water and then with a low alkanol; 
     (c) next, the product is crystallised during further stirring, and 
     (d) the crystalline product obtained is sucked off, washed and dried. Furthermore, the invention relates to a commercial mixture thus prepared to produce copolycondensable flameproofing agents for polyester fibers by directly reacting the mixture with itaconic acid or itaconic acid compounds, optionally together with one or more diols.

This application was filed under 35 U.S.C. 371 and is the National Stageof International Application No. PCT/EP96/02715, filed Jun. 21, 1996.

The tautomeric compounds (6H)-dibenzo-(c,e)(1,2)-oxaphosphorin-6-one(=9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), usually referredto as "DOP" in the field, and6-hydroxy-(6H)-dibenzo-(c,e)(1,2)-oxaphosphorine are known compounds,the reaction products of which with itaconic acid, itaconic acid esteror itaconic acid anhydride are widely used as copolycondensableflameproofing agents for polyester fibres. Copolycondensableflameproofing agents for polyester fibres are incorporated directly intothe polyester chain during the polymerisation of the polyester andthereby become an integral constituent of the polyester chain. Theflameproofing agents fixedly incorporated into the polyester fibres areby nature far superior to those flameproofing agents with whichpolyester fibres are subsequently finished. The preparation of the saidDOP/itaconic acid derivatives and the use thereof is described in Germanpatent specification no. 26 46 218, for example.

German patent no. 20 34 887 discloses a process for the preparation ofDOP and the preparation of 2'-hydroxydiphenyl-2-phosphinic acid, ahydrolysis product of DOP, wherein o-phenylphenol is reacted underreflux with phosphorus trichloride in the presence of a Lewis acid as acatalyst, with the release of hydrogen chloride, and the resultingreaction mixtures are hydrolysed, after which crystalline products areultimately obtained. However, none of the modifications of the processdisclosed in the named patent was satisfactory for the preparation ofDOP on a commercial scale, in particular for reasons of safety in theworkplace, environmental protection and the cost of the apparatus neededto carry out the process.

In a modification of the known process (example 1), phosphorustrichloride and o-phenylphenol are gradually heated to 140° C. in afirst step. After the release of hydrogen chloride is complete, zincchloride is added as a catalyst, and one gradually heats to 210° C. in asecond step. The reaction product must then be high-vacuum distilled(195° C., 20 torr) in a third step. Therefore, for production on acommercial scale, the entire production plant must meet the prescribedsafety requirements for high-vacuum operation.

In another modification of the known process (examples 2 and 3), thefirst step of the process is carried out as a one-pot reaction; in thesecond step, however, an excess of phosphorus trichloride must thensubsequently be added over a period of 15 hours, which is associatedwith considerable safety-related expenditure on account of theharmfulness of this chemical. After that, the mixture must be heated to200° C. to 230° C. and then be high-vacuum distilled.

Hydrolysis of the initially formed6-chloro-(6H)-dibenzo-(c,e)(1,2)-oxaphosphorine is carried out by theknown method either by pouring the oily residue from high-vacuumdistillation directly onto ice or into a sodium carbonate solution, towhich activated carbon has been added. Both hydrolysis variations areunsatisfactory, with respect to both the yield and the necessaryfinishing steps (recrystallisation, filtration).

European patent application EP-A-0 582 957 discloses a process for thepreparation of 6-chloro-(6H)-dibenzo-(c,e)(1,2)-oxaphosphorine, whereino-phenylphenol and the catalyst are heated to 180° C. while beingstirred. The phosphorus trichloride is then charged to the mixture at atemperature between 170° C. and 220° C. within 8 to 20 hours. Theresulting crude product can be directly further processed, e.g. as a 50%solution in toluene or xylene.

However, as phosphorus trichloride is generally used in excess tooptimise yields, vacuum distillation (165° C., 0.17 kPa) also has to becarried out in this known process.

The object of the invention is to improve a process for the preparationof 2'-hydroxydiphenyl-2-phosphinic acid in the form of a commercialmixture with 6-hydroxy-(6H)-dibenzo-(c,e)(1,2)-oxaphosphorine, whereino-phenylphenol is reacted under reflux with phosphorus trichloride inthe presence of a Lewis acid as a catalyst, with the release of hydrogenchloride, and the resulting reaction mixture is hydrolysed, after whichthe product is crystallised and then separated, in such a manner that,even on a commercial scale, it does not require a distillation step, inparticular a high-vacuum distillation step, and requires littleapparatus, but nevertheless produces a high yield of a crystallineproduct of sufficient purity.

According to the invention, this object is achieved in that, in areactor fitted with a reflux condenser and a stirrer, a one-pot reactionis carried out without isolating intermediate products comprising thesteps:

(a) a mixture of PCl₃ and a catalyst is formed and o-phenylphenol isadded thereto while simultaneously heating the reaction mixture, and thereaction mixture is then refluxed;

(b) the resulting reaction mixture is allowed to cool and, duringcontinuous stirring, is mixed first with water and then with a loweralkanol;

(c) next, the product is allowed to crystallise during further stirring,and

(d) the crystalline product obtained is sucked off, washed and dried.

By combining said measures, the commercial mixture can, surprisingly, beprepared with a high yield and with sufficient purity for furtherprocessing, in particular direct conversion into itaconic acidderivatives for the production of copolycondensable flameproofing agentsfor polyester fibres, without a distillation step, without the expenseassociated with high-vacuum apparatus, without the necessity of heatingto above 200° C. and without protective sluices for the subsequentdropwise addition of phosphorus trichloride.

Advantageous embodiments of the process according to the inventionconsist in that the PCl₃ is introduced at a temperature between 60° C.and the boiling temperature of the reaction mixture (pure phosphorustrichloride boils at 74.5° C. under normal conditions), in that thereaction mixture is heated in step (a) to a temperature between 80° C.and 160° C. and in that the reaction mixture is held under reflux for atleast a further 3 hours after all the o-phenylphenol has been added.

The reaction mixture is preferably held under reflux for at least afurther 3 hours at a temperature between 140° C. and 160° C. after allthe o-phenylphenol has been added.

For good crystallisation of the product, it is furthermore preferable ifthe reaction mixture in step (b) is allowed to cool to a temperaturebetween 30° C. and 50° C.

Zinc chloride is preferably used as a catalyst, and methanol, ethanol,n-propanol or isopropanol is preferably used as a lower alkanol.

With respect to the preferred further processing of the commercialmixture to form copolycondensable flameproofing agents for polyesterfibres, it is advantageous if, in step (d), the sucked-off crystallineproduct is washed free of chloride with water and then dried.

Optimum yields are obtained when PCl₃ and o-phenylphenol are reactedtogether in a molar ratio of 1:1 to 1:1.5, preferably 1:1.25 to 1:1.35.

A further subject of the invention is a commercial mixture, prepared bythe process according to the invention, for producing copolycondensableflameproofing agents for polyester fibres by directly reacting thismixture with itaconic acid, an itaconic acid ester or itaconic acidanhydride, optionally together with one or more diols.

The course of the reaction in the process according to the invention isexplained in further detail with the aid of the reaction diagram below:

Firstly, o-phenylphenol (1) reacts with PCl₃, eliminating 1 mole ofhydrogen chloride (HCl). The ester (2), formed as an intermediateproduct, cyclises with the aid of zinc chloride, used as a catalyst, toform 6-chloro-(6H)-dibenzo-(c,e)(1,2)-oxaphosphorine (3), releasing afurther mole of hydrogen chloride. Hydrolysis of the dihydrophenanthrenederivative (3) initially produces6-hydroxy-(6H)-dibenzo-(c,e)(1,2)-oxaphosphorine (4)--which is intautomeric equilibrium with (6H)-dibenzo-(c,e)(1,2)-oxaphosphorin-6-one(4')--eliminating a third mole of hydrogen chloride. Further hydrolysisof this compound (4) or (4'), also known as "DOP", in the presence of alower alkanol finally leads to ring fission, producing2'-hydroxydiphenyl-2-phosphinic acid (5).

EXAMPLE

102.6 l (161.5 kg; 1176.47 moles) PCl₃ and 1.635 kg (12 moles) ZnCl₂ areintroduced into a reactor, fitted with a reflux condenser and a stirrer,at a temperature of 70° C. 200 kg (1176.47 moles) o-phenylphenol areadded to this mixture with the addition of heat, and the reactionmixture is refluxed. During the course of this, the reaction solutionreaches a temperature of approximately 150° C. Hydrogen chloride gas isliberated and is collected in an absorber filled with water. After 5 to6 hours, the o-phenylphenol has largely reacted, the reaction solutionhaving gradually turned yellow.

The reaction solution is allowed to cool to 40° C. to 50° C. and 21.17 lwater are then added, stirring continuously. Hydrogen chloride gas isonce more released and collected in an absorber. A further 78 l waterand 156 l ethanol are then added during further stirring and with theaddition of heat, which ensures that a temperature of approximately 50°C. is maintained. During cooling, the product crystallises. It isfiltered off via a suction filter, washed free of chloride with waterand dried. A commercial mixture of 2'-hydroxydiphenyl-2-phosphinic acidand 6-hydroxy-(6H)-dibenzo-(c,e)(1,2)-oxaphosphorine is obtained in theform of a white crystalline powder. Yield: 85%. ##STR1##

We claim:
 1. A process for the preparation of2'-hydroxydiphenyl-2-phosphinic acid in the form of a commercial mixturewith 6-hydroxy-(6H)-dibenzo-(c,e) (1,2)-oxaphosphorine, whereino-phenylphenol is reacted under reflux with phosphorus trichloride, inthe presence of a Lewis acid as a catalyst, with the release of hydrogenchloride, and the resulting reaction mixture is hydrolyzed, after whichthe product is crystallized and then separated, characterized in that,in a reactor fitted with a reflux condenser and a stirrer, a one-potreaction is carried out without isolating intermediate productscomprising the steps: (a) a mixture of PCl₃ and a catalyst is formed ando-phenylphenol is added thereto while simultaneously heating thereaction mixture, and the reaction mixture is then refluxed;(b) theresulting reaction mixture is allowed to cool and, during continuousstirring, is mixed first with water and then with a lower alkanol; (c)next, the product is allowed to crystallize during further stirring; and(d) the crystalline product obtained is sucked off, washed and dried. 2.The process of claim 1, wherein said PCl₃ is introduced at a temperaturebetween 60° C. and the boiling temperature of the reaction mixture. 3.The process of claim 1, wherein the reaction mixture is heated in step(a) to a temperature between 80° C. and 160° C.
 4. The process of claim1, wherein the reaction mixture is held under reflux for at least afurther 3 hours after all the o-phenylphenol has been added.
 5. Theprocess of claim 4, wherein the reaction mixture is held under refluxfor at least a further 3 hours at a temperature between 140° C. and 160°C. after all the o-phenylphenol has been added.
 6. The process of claim1, wherein the reaction mixture in step (b) is allowed to cool to atemperature between 30° C. and 50° C.
 7. The process of claim 1, whereinzinc chloride is used as a catalyst.
 8. The process of claim 1, whereinmethanol, ethanol, n-propanol or isopropanol is used as said loweralkanol.
 9. The process of claim 1, wherein, in step (d), saidsucked-off crystalline product is washed free of chloride with water andthen dried.
 10. The process of claim 1, wherein PCl₃ and o-phenylphenolare reacted together in a molar ratio of 1:1 to 1:1.5, preferably 1:1.25to 1:1.35.
 11. A process for the preparation of2'-hydroxydiphenyl-2-phosphinic acid in the form of a commercial mixturewith 6-hydroxy-(6H)-dibenzo-(c,e) (1,2)-oxaphosphorine, whereino-phenylphenol is reacted under reflux with phosphorus trichloride, inthe presence of a Lewis acid as a catalyst, with the release of hydrogenchloride, and the resulting reaction mixture is hydrolyzed, after whichthe product is crystallized and then separated, characterized in that,in a reactor fitted with a reflux condenser and a stirrer, a one-potreaction is carried out without isolating intermediate productscomprising the steps of:(a) a mixture of PCl₃ and a catalyst is formedand o-phenylphenol is added thereto while simultaneously heating thereaction mixture, and the reaction mixture is then refluxed, with saidPCl₃ being introduced at a temperature between 60° C. and the boilingtemperature of said reaction mixture, said reaction mixture being heatedto a temperature of between 80° C. and 160° C. and held under reflux forat least a further 3 hours after all the o-phenylphenol has been added;(b) the resulting reaction mixture is allowed to cool and, duringcontinuous stirring, is mixed first with water and then with a loweralkanol; (c) next, the product is allowed to crystallize during furtherstirring; and (d) the crystalline product obtained is sucked off, washedand dried.
 12. The process of claim 11, wherein the reaction mixture isheld under reflux for at least a further 3 hours at a temperaturebetween 140° C. and 160° C. after all the o-phenylphenol has been added.13. The process of claim 11, wherein the reaction mixture in step (b) isallowed to cool to a temperature between 30° C. and 50° C.
 14. Theprocess of claim 11, wherein zinc chloride is used as a catalyst. 15.The process of claim 11, wherein methanol, ethanol, n-propanol orisopropanol is used as said lower alkanol.
 16. The process of claim 11,wherein, in step (d), said sucked-off crystalline product is washed freeof chloride with water and then dried.
 17. The process of claim 11,wherein PCl₃ and o-phenylphenol are reacted together in a molar ratio of1:1 to 1:1.5, preferably 1:1.25 to 1:1.35.
 18. A process accordingly toclaim 1, and including the step of: (e) reacting to crystallized productobtained in step (d) with itaconic acid, an itaconic acid ester oritaconic anhydride.
 19. A process according to claim 18, wherein one ormore diols is included in the reaction step (e).
 20. A processaccordingly to claim 11, and including the step of: (e) reacting thecrystallized product obtained in step (d) with itaconic acid, anditaconic acid ester or itaconic anhydride.
 21. A process according toclaim 20, wherein one or more diols is included in the reaction step(e).